Patio process

The patio process is a process for extracting silver from ore. The process was invented by Bartolomé de Medina in Pachuca, Mexico, in 1554. The patio process was the first process to use mercury amalgamation to recover silver from ore. It replaced smelting as the primary method of extracting silver from ore at Spanish colonies in the Americas. Other amalgamation processes were later developed, importantly the pan amalgamation process, and its variant, the Washoe process. The silver separation process generally differed from gold parting and gold extraction, although amalgamation with mercury was also sometimes used to extract gold.

Bartolomé de Medina was a successful Spanish merchant who became fascinated with the problem of decreasing silver yields from ores mined in Spanish America. By the mid-sixteenth century, it was well known in Spain that American silver production was in decline due to the depletion of high-grade ores and increasing production costs. The New Laws, prohibiting the enslavement of Indians, had resulted in higher labor costs as miners turned to wage labor and expensive African slaves. These higher production costs made mining and smelting anything but the highest grade silver ores prohibitively expensive, just as the availability of high grade ores was in decline. Bartolomé de Medina initially focused his attentions on learning about new smelting methods from smelters in Spain. He was approached during his research by an unknown German man, known only as "Maestro Lorenzo," who told him that silver could be extracted from ground ores using mercury and a salt-water brine. With this knowledge, Medina left Spain for New Spain (Mexico) in 1554 and established a model patio refinery in order to prove the effectiveness of the new technology. Medina is generally credited with adding "magistral" (a copper sulfate) to the mercury and salt-water solution in order to catalyze the amalgamation reaction. However, some historians assert that there were already sufficient copper sulfates in the local ores and that no additional magistral was needed. Regardless of whether or not Medina's contribution was entirely original, he promoted his process to local miners and was able to obtain a patent from the Viceroy of New Spain. As a result, he is generally credited with the invention of silver amalgamation in the form of the patio process.

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